The left-handed Anderson was initially placed on the 15-day disabled list May 1 with a sprained right ankle, two days after he aggravated it by pitching 5 1/3 relief innings in Oakland's 19-inning win over the Angels. He made a rehab start with Double-A Midland on Sunday and came out of the outing rather encouraged, only to experience some pain when doing fielding drills Tuesday.
"When he did those yesterday and ran around a little bit, he felt it some," Melvin said. "The strange part of it is that he's not feeling it when he pitches. He threw his bullpen, didn't feel it at all. Felt it more so when we were doing drills. It's just not at the point where we're comfortable putting him out on a big league mound again and going through what we have been the last couple of times."
Anderson is now likely to rest the ankle until the discomfort subsides. He'll continue to keep his arm in shape, but he will be limited in other activities, making it unclear when the A's will consider slotting him back into the rotation.
In the meantime, Wednesday starter Dan Straily is likely to remain in Anderson's spot.
"I know it's frustrating for him, but it's the right thing to do," Melvin said. "He wants to pitch, but he also understands that he's not ready to at this point."
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.